2010 Gen 3 Prius and 12V Battery Question

I followed the notes provided by Cproaudio larger battery modification. Group 25
Requires one hole drilled on the battery tray, to move it back to the already provided set of OEM bolt holes.
Just follow his instructions if you are interested.
HERE

 

The 12 volt battery gets charged by the DC/DC converter, constantly on when the car is READY. The ICE doesn't need to start for that (until enough charge has been used from the HV battery for the ICE to start to top that off).

The computer usually likes to keep the HV battery in a window of about 40% to 60% charge, so (assuming no other reason to run) the ICE will cycle every time about 20% of HV charge is lost. (I've seen it sometimes shorten the cycle to 10%, that is, ICE on around 40% but shut off around 50% instead of 60%).

Figuring the HV battery at about 1.3 kilowatt-hours, 10 to 20 percent of that is 130 to 260 watt-hours.

The nominal charge rate for the 12 volt battery is 5 amps or less—60 watts or less—so (disregarding other loads), keeping the 12 V battery charged would start the ICE every two to four hours or so.

The picture could change if the old, tired battery ends up drawing a lot more than 5 amps, and that would be an interesting thing to measure, but to my knowledge nobody has. I know not everybody has a clamp meter, but it would be great if somebody, who is about to replace their 12 volt because they think it is drawing too much, could take a minute to measure that draw before replacing it.

It would be super easy to do, because the charge rate doesn't even depend on engine speed as it does in ordinary cars. It's constant. Just put car in ready, clamp meter on cable, read amps, done.

And all of PriusChat would have new useful information about something that's very often talked about.

-Chap

 

It's a CTEK charger? My manual says to use recondition maybe once a year. Since I'm charging frequently I don't use the recondition, just the "snowflake" symbol. I think recondition is a little more aggressive, to the point of "bubbling" it a bit? But yeah in your case sounds like a good idea for the first charge.

Appreciate: I'm a layman at charging, don't really understand the science.

 

Ok left to charge from 7pm to 4am ...the ctech was at number 7 meaning fully charged....
I reconnected the battery....I checked the voltage using the on-screen self diagnostic (no ready light) and it shows 11.3v
?

Posted via the PriusChat mobile app.

 

Something might be off. If the CTEK completed its regimen I think that means it's happy with the battery's condition. You don't have a digital multimeter? Whenever I've measured a battery with a MM, after charging thus. It'll be around 13.0 volt, due to what they call surface charge. A day later with a bit of driving, settle down to around 12.7.

For starters try a MM if you can. It might be flogging a dead horse, but CTEK completing the cycle without complaint makes me wonder if it's your measurement method.

 

Stopped at the local garage,asked for a load test .....10.5v

Posted via the PriusChat mobile app.

 

That again is another value, not the "at rest" voltage. Load test, well a traditional load test, is what the voltage drops to when a load is applied. 10.5 under that condition might be actually not bad, I'm not sure.

FWIW, what I use for a load test, and it can also show the at rest voltage, is Solar BA5. You tell it what type of battery you have, the specified cold crank amps (or crank amps, or several others), run the test, it tells you actual CCA and gives a verdict.

But anyway, a cheap multi meter (digital display) on volt setting, cheapest first step to getting a rudimentary assessment.

 

Are there any directions for bridging the 12v connection or somehow preserving the computer and nav settings when changing the 12v? Seems i've read of some issues for people directly after changing 12v due to computer reset that I'd rather avoid.

I've done some searching and couldnt find anything on this topic.

Just checked my 12v via the diagnostic screen (after sitting 3 days in the cold) and its reading 10.9v on accessory mode with headlights off (just a single press of the on button without foot on brake). I'm thinking that means need to replace now.

 

"I've done some searching and couldnt find anything on this topic."

That's because there ISN'T anything to find...You're just gonna have to deal with it.

 

Off the topic a bit, there is an offset between the screen reading and the battery post reading. It is better to measure the voltage directly on the posts.

With that said, your battery voltage does look low.

 

Thanks - I will check it directly at the battery with my multimeter (unless I can check it somehow at the jump points in the front of the car?)

 

At the jump points should be about the same, barring a loose connection somewhere.

 

Yep check it the same way you would jump the car. You'll get a more accurate reading there.

Fwiw, 10.9 at the diagnostic menu does seem rather low. Have you tried hooking it up with a trickle charger yet?

 

FWIW, ours spends more time (by far) on than off a charger (CTEK 4.3 with quick connect). Pretty much necessity with our sporadic usage. The car gets occasional good runs, but typically sits 2~4 days (or more) between uses, and sometimes it’s just milk runs.

 

When I replaced my 12V battery I connected another battery first using jumper cables to the jumper connection under the hood at the fuse box. (So that's three batteries in play: the old one, the replacement, and the jumper.) Worked fine.

 

Luckily I still have an old one I pulled out of my gen 2 about 4 months ago. Probably still has a bit of juice in it. I will try that.

 

My Gen 2 prius battery lasted 8 years of my driving habits so its probably not worth it to me (cost wise, and hassle-wise) to buy a battery charger like that. My car does sometimes go 2-3 days without being driven but most days it at least goes for a short 2-5 km jaunt around town. It might be a good thing to have around, especially to charge old batteries up.

I am assuming that this 2010 Prius I just bought is on its original battery - unless battery replacement is part of Toyota dealership scheduled maint the previous owners wouldnt have been the type of people to proactively replace it. Also my OBD scanner showed that no codes had been cleared or reset in the last 100,000 kms, so I am wondering if that also could signify that the battery is at least that many km's old.

 

Okay here are the measurements I got on my 12v. Interesting that the dagnostic screen was showing about 1.0 volt lower than when using my multimeter on the battery terminals at the back of the car.

After car was off for 3 days (ambient temp -2 degrees C):
Car turned off:
11.84 (multimeter)

Accessory mode:
10.7 (diagnostic screen)

Car Turned on:
14.80 (multimeter)
14.0 (diagnostic screen

Drove car for 30 minutes, turned off for 1 hour (ambient temp 4 degrees C):
Car turned off:
12.32 (multimeter)

Accessory Mode:
11.3 (diagnostic screen)

Car Turned on:
14.80 (multimeter)
14.0 (diagnostic screen


Muti-meter makes battery look a bit better than diagnostic screen. Interestingly the battery is a "Toyota Genuine Parts" battery (not a Yuasa - maybe its a rebrand?) and there are date circles that are supposed to be punched on the label when installed but they arn't punched on mine. I dont really have a way of telling how old this battery is. I've attached a photo of it.

 

If the car was "off", how did you get to the diagnostic screen?

I think you can only get there in ACC or ON (or in READY, which of course you've already reported).

Between ACC and ON, ON will pull the displayed voltage down a bit more than ACC does; the car is powering more things in ON.

 

Do you have two cords running to your car or did you rig a way to join the charger with your block heater into one plug?